Natural History of Yolcanos and Earthquakes. 49 



mountain has sunk in consequence of a subterranean shock 

 which took place before the discovery of Amej^ica. At the pres- 

 ent time Capac-Urcu is lower than Chimborazo, Boussingault 

 alludes to many instances, in which it is asserted^ that the Cor- 

 dilleras have sunk. Without taking into consideration the infer- 

 ences drawn from barometrical measurements, made by Bous- 

 singault and his predecessors, which seem indeed to confirm that 

 supposition, we will only mention the following circumstances. 

 The French academicians, who, a century ago, were sent to 

 Quito for the purpose of determining the form of the globe, were 

 very much embarassed in tlieir station on GuaguapirhivrJia^ by 

 the snow surrounding their signals. Now, for many years, no 

 snow has been found on the summit of this mountain. The in- 

 habitants of Popayaii have also remarked, that the inferior limit 

 of the snow covering the Purace is gradually rising, whilst the 

 mean temperature has remained the same for the last thirty 

 years, whence Boussingault infers, that the Purace is sinking 

 down. 



That masses thrown up in a state of igneous fusion sink again 

 by degrees, in consequence of their consolidation and contraction, 

 cannot be doubted. But even if their elevation had taken place 

 in a solid state, yet the immense masses of the Andes have risen 

 from depths, where a pretty high temperature prevails. Suppos- 

 ing the Andes to have risen 24,000 feet in height, that part of 

 them which is now at the level of the sea, must have been be- 

 fore the elevation so many thousand feet below it. This part 

 brought, therefore, with itself from beneath, a temperature which 

 was ■' ^ n — 470^ F. higher than that which existed at the level 



^ 



of the sea before the elevation. The same holds good of each 

 part of the Andes, in any depths, so that every where in erupted 

 masses the temperature surpassed that of the adjacent rocks by 

 470^^ F. Whilst now these masses gradually lost their surplus 

 of heat, they were contracted. But this cooling of these masses 

 can as far as they are within the earth, only be affected by con- 

 duction, therefore a long period will elapse for that purpose. 

 That part of the Andes, which is elevated above the surface of 

 the earth, and is exposed to the atmosphere, will of course cool 

 a little more quickly. If the bases of the rocks thrown up be at 

 a <^reat depth below the surface, their contraction in consequence 

 of^ their cooling may be very considerable, and as the elevation 



Vol. xx&vii, No. l.-July, 1839; bis. 7 



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